High-dynamic image sensor

Abstract

The invention proposes an image sensor having a functional architecture and an optimized pixel structure for promoting easy high-dynamic reconstruction without compromising on compactness. The image sensor uses a structure of pixels (fig.2) that vertically share, in pairs, at least one read node, and comprises a memory node for temporarily storing charges. The image sensor provides a layout of thepixel control rows such that commands to transfer charges (TRA) from the photodiode (PH) to the memory node (MN) apply vertically, to the pixels of one and the same column, and the other signals apply horizontally to the pixels of one and the same row, and said vertical transfer command rows are driven so as to apply two different exposure times, one to the even columns and the other to the odd columns. The pixels and the read circuit are driven so as to perform one read operation per vertical pair of pixels, which supplies a digital value (Vr) that represents the analogue sum of the chargesintegrated by the two pixels of the pair, over the exposure time associated with the column of the pair. A digital processing block is configured so as to calculate, for each vertical pair of pixels,an interpolated digital value (Vir) corresponding to the other exposure time, and select the value from the one associated with the long exposure time and the one associated with the short exposure time as high-dynamic digital value through comparison with at least one threshold. A periodic pattern of coloured filters makes it possible to create an HDR-mode colour image sensor, by defining a macro-pixel covering 4 blocks of 2 by 2 pixels, with one block per coloured filter colour of the pattern, promoting additional horizontal grouping in each block.

Description

technical field [0001] The present invention relates to an active pixel image sensor (with a pixel structure of a photosensitive element and a control transistor) capable of providing an output image with a high dynamic range, and is especially suitable for scenes requiring extremely high-contrast images. Background technique [0002] The dynamic range characteristics of an image sensor reflect its ability to simultaneously capture unsaturated signals in extremely bright areas and significant signals (above noise) in dark areas in the same image. This dynamic range is inherently dependent on the pixel architecture (circuit diagram and technology) and the properties of the associated sensor's pixel readout circuitry (gain, read noise, converter output depth). In the exposure conditions of very high contrast scenes, the inherent limitation of the sensor's dynamic range manifests itself as a loss of information: if the exposure time is short, it does not saturate very quickly, ...

AI Technical Summary

Problems solved by technology

However, since it is also desirable to utilize CDS readout technology to reduce the noise ratio, the pixel structure is disadvantageous both in terms of size and opening ratio

A pixel structure with shared elements can improve both aspects, but it will complicate the sequencing signal management for obtaining HDR images according to the existing technology

Color management adds additional complexity to all these different aspects

Images